Toxicity of 6PPD-quinone in European seabass (Dicentrarchus labrax) under baseline and Vibrio alginolyticus challenge conditions: Protective insights from astaxanthin mitigation.

6PPD-quinone, a widespread pollutant from tire wear, exhibits species-specific toxicity in aquatic organisms. This study examines the effects of 6PPD-quinone on European seabass (Dicentrarchus labrax) at an environmentally relevant concentration (2.85 μg/L, static renewal for five days) under both unchallenged conditions and bacterial challenge with Vibrio alginolyticus. The study also evaluates the hepatoprotective and immunomodulatory potential of astaxanthin supplementation (150 mg/kg diet for 30 days), derived from non-GMO Haematococcus pluvialis microalgae. While 6PPD-quinone exposure (up to 250 μg/L for 72 h) did not cause mortality, it induced neurological symptoms, including erratic swimming and respiratory distress. At 2.85 μg/L, biochemical analyses showed increased albumin, altered creatine kinase and blood urea nitrogen levels, and disrupted glucose homeostasis. Significant hepatic and gill lesions, such as diffuse hepatic necrosis and lamellar fusion, were observed. Astaxanthin mitigated liver necrosis, reduced inflammation, restored albumin/globulin ratios, and maintained glucose and triglyceride homeostasis. It improved gill integrity, reduced blood urea nitrogen, and enhanced lysozyme activity while preventing excessive immune activation. 6PPD-quinone disrupted immune gene expression in the head-kidney and spleen, which astaxanthin modulated. This study highlights 6PPD-quinone's physiological impact on seabass and astaxanthin's potential in mitigating pollutant toxicity, emphasizing that balanced immune responses are essential for maintaining health under environmental stressors.